The oil & gas industry regularly employs seismic reflection surveys to image the earth's subsurface, looking for geologic structures and environments capable of generating, migrating, and trapping commercial hydrocarbon deposits. Geoscientists use two dimensional (2D) and three dimensional (3D) seismic sections and volumes to more fully define geologic structural and stratigraphic features commonly associated with hydrocarbon discoveries, such as subsurface faults, unconformities, channels, and submarine fans. The slices and volumes are built from reflection survey data collected from a section or volume of the subsurface. Today, 3D seismic is increasingly being employed to detect and map natural fracture systems that can greatly influence the effective permeability of producing reservoirs, thereby affecting the overall economics of developing oil & gas fields.
Seismic reflection surveys are performed using sensors placed on land, in the sea, and on the sea floor. Received reflections are noise-filtered and the data are otherwise conditioned for interpretation. A typical record of seismic echoes as detected by a single receiver at the surface is a trace in the shape of a sinusoidal curve as a function of time. Seismic echoes oscillate between compression and rarefaction over a period of several seconds, and this rise and fall in pressure with time is recorded for processing and analysis. The amplitude generally reflects the nature of the formation, while the time generally reflects the depth below the receiver. A seismic trace may be subject to multipath, interference, echoes and other effects that reduce the accuracy of the trace. As a result the traces are filtered, conditioned, and interpreted. An interpreter may have several thousand or several million traces to interpret in a single survey.
One element of interpreting subsurface rock and fluid characteristics as well as the presence of faults and channels is the analysis of properties of the recorded seismic waveforms known as seismic attributes. Various attributes may be determined in a variety of different ways from elements of the seismic waves themselves, such as amplitude, phase, frequency, and attenuation. There are also attributes associated with the differences in adjacent recorded waveforms such as similarity or semblance, discontinuity, and attenuation. These latter attributes are more typically used to identify changes from one recorded signal to another. As a result they reveal subtle structural and stratigraphic features within a 2D slice or 3D seismic volume such as faults, fractures, channels, and salt domes.